I think that's because A.) it's natural homerism and B.) the Chiefs' victories have been more impressive.
The Chiefs and Bucs are both 2-0 and neither were expected to be 2-0 so you've got plenty of folks doing the "Which 2-0 is team is for real?" and "Which 2-0 team is a fraud?" type of questions.
Here's who they have played:
Chiefs opponents: Chargers (1-1) and Browns (0-2)
With one common opponent wiped out, it's clear that beating the Chargers is a much more impressive win than beating the Panthers.
Neither the Chiefs nor the Bucs had any known strengths entering this season. There are a lot of new parts. For the Chiefs, I suppose it'd be the run game and the defense. For the Bucs, it'd be the defense, even though they weren't expected to be this good through two games.
The Chiefs can stop the run (9th in the NFL) and can run the ball (5th in the NFL). Those are two very important factors in winning NFL games. For that reason, I'm going to say the Chiefs are a better team right now. I feel like they have more playmakers (Jamaal Charles, Dexter McCluster, Javier Arenas) and a well-coached defense.
But in the future? The Chiefs have to find out who they have at quarterback because the Bucs have their man in Josh Freeman and, frankly, he looks better than Matt Cassel at this point.